Paper material for pressure sensitive recording system

ABSTRACT

A paper material for the pressure sensitive recording system is formed of a fibrous material, at least a part of which is synthetic one. The support sheet has a small oil penetration rate so that the smudge due to penetration of oil containing a dye material may be prevented to the utmost extent. Preferably the synthetic fibrous material used for forming the support sheet has a specific surface area of at least 0.7 m2/g for increasing the brightness and the opacity of the support paper.

' United States Patent [191 Masaoka et al.

[451 Nov. 215, 1975 I 1 PAPER MATERIAL FOR PRESSURE SENSITIVE RECORDING SYSTEM [75] Inventors: Takashi Masaoka, I-lyogo; Noritoshi Y Watanabe, Osaka; Yasuo Takegawa; Tojiro Kitahori, both of I-Iyogo, all of Japan [73] Assignee: Kanzaki Paper Mfg. Co. Ltd., 7 Tokyo, Japan [22] Filed: July 19; 1973 [21] Appl. No.: 380,662

[30] Foreign Application Priority Data July 21, 1972 Japan 47-73524 [52] U.S. Cl. 428/323; 427/145; 427/150; 427/261; 428/341', 428/454;

[51] Int. Cl. B41C 1/06; B41M 5/16 [58] Field of Search 117/367, 36.1, 36.3, 36.8; 161/162; 428/323, 341, 454, 511, 513

[56] References Cited UNITED STATES PATENTS 2,730,456 1/1956 Green et al. ll7/36.1

2,730,457 1/1956 Green et a1 ll7/36.8 3,167,443 1/1965 McHugh et a1... 117/36.7 3,635,747 1/1972 Skees et al 117/363 3,728,210 4/1973 Piron 161/162 OTHER PUBLICATIONS IBM Technical Disclosure Bulletin, Vol. 5, No. 4, Sept. 1962.

Primary Examiner-Thomas J. Herbert, Jr. Attorney, Agent, or FirmCushman, Darby & Cushman [57] ABSTRACT 16 Claims, NoiDrawings kylnaphthalene,

PAPER MATERIAL FOR PRESSURE SENSITIVE RECORDING SYSTEM BACKGROUND OF THE INVENTION This invention relates to a pressure sensitive recording system and more particularly to a paper materal for the pressure sensitive recording system.

There are known several types of pressure-sensitive recording system utilizing an electron donor-acceptor color-forming reaction between a colorless dye material and a color forming reactant acid material. The colorless dye material and the color forming reactant acid material are hereinafter referred to as color former" and color acceptor,respectively. Those pressure-sensitive recording systems comprise a support sheet having, disposed on at least one surface thereof, microcapsules containing oil droplets in which a color former is dissolved and/or a color acceptor capable of producing color when brought into reactive contact with the color former.

For example U.S. Pat. No. 2,730,456 discloses a transfer-copy system wherein minute oil droplets in which a color former is dispersed or dissolved are encapsulated and coated onto a transfer sheet. The color former is thereafter transferred to a receiving sheet by rupturing said capsules. The underlying receiving sheet has a color reactant coating thereon containing a color acceptor which will react with the color former causing a visible colored mark at points where the microcapsules have been ruptured and the color former has been transferred. In case when multiple copies are needed at least one intermediate copy sheet having said microcapsules and said color acceptor on the opposite surfaces thereof, respectively, is interposed between the upper copy sheet and the underlying copy sheet.

US. Pat. No. 2,730,457 discloses another type of a pressure-sensitive record sheet. In this pressure-sensitive record sheet, there are disposed on one surface of the same sheet both the color acceptor and the cap sules containing oil droplets in which the color former is dissolved. This record material is known as a self contained system.

Among the color formers which are preferably used, there are crystal violet lactone, benzoyl leucomethylene blue, malachite green lactone, rhodamine lactone, fluoran derivatives, spironpiran, mixtures thereof and etc.

Among the solvent oils for dissolving the above color formers, there are included non-volatile oils such as alalkylbiphenyl, diarylmethane, terphenyl derivatives, dibenzylbenzene, liquid paraffin, castor oil, olive oil, rape oil and cotton seed oil.

Among the color acceptors there are known inorganic compounds such as acid clay, activated clay, bentonite, kaolin, zinc oxide, zinc hydroxide, zinc carbonate and etc. and organic compounds such as aromatic carboxylic acids, multivalent metallic salts of aromatic carboxylic acids, aromatic carboxylic acid polymers, multivalent metallic salts of aromatic carboxylic acid polymers, phenols, phenol polymers, multivalent metallic salts of phenol polymers mixtures thereof and etc.

As for the support sheet material for the above mentioned pressure sensitive recording systems, natural fiber papers have been in practical use because of their easy convertibility and economical availability. Since it is desirable to reduce the weight or thickness of the paper for the multiple copying, there have been used papers having such a light weight as within the range of about 30 to 50 g/m The pressure sensitive recording paper utilizing such a light weight support sheet like this has some inevitable disadvantages. That is, an incidental rupture of microcapsules during storing or transporting the products will produce the so-called smudges on the opposite surface of the recording paper or on a surface of the other sheet superposed since the oil containing a color former penetrates through the support sheet and the color former reacts with the color acceptor disposed on the opposite surface or on the surface of another superposed sheet facing to said opposite surface. The lighter the weight of the paper, the lower both the brightness and the opacity of the paper. This will result in that the contrast of the color image is reduced and the color image becomes to be seen through the sheet from the opposite side. In addition the lighter the weight of the paper, the greater the sensitivity of the paper to the humidity. This will cause troubles of curling, expansion and contraction of the paper. The curling of the paper is disadvantageous in the steps of manufacturing the pressure sensitive recording papers, especially, in the steps of coating and winding as well as in the practical use.

The primary object of the invention is to provide an improved paper material for the pressure sensitive recording system in which the above mentioned disadvantages can be avoided. Particularly one of the objects of the invention is to provide an improved paper material for the pressure sensitive recording system in which the so-called smudge which will be caused during storing and transportating the products can be prevented.

Another object of the invention is to provide an improved paper material for the pressure sensitive recording system which has a good brightness and opacity as required.

A further object of the invention is to provide an improved paper material for the pressure sensitive recording system which has an improved dimensional stability against humidity.

A still further object of the invention is to provide an improved paper material for the pressure sensitive recording system which is relatively light in addition to the above mentioned advantages.

Other objects and advantages of the invention will be partly apparent and will be partly discussed in detail hereinbelow.

SUMMARY OF THE INVENTION The paper material for the pressure sensitive recording system according to the invention comprises a support sheet having, disposed on at least one of the surface thereof, at least one color producing reactant selected from the group consisting of a color former which is dissolved in an oil and contained in microcapsules and a color acceptor reactive with said color former to produce a color image. The support sheet is formed of a fibrous material. A part of the fibrous material is synthetic one. The support sheet has a COEITICI' ent of tetralin penetration rate of 600 X 10 cm/min" or less. The coefficient of tetralin penetration rate is represented by K in the following formula:

11 (cm) =K WES wherein h is a length by cm of tetralin penetration and t is time by minute.

In a preferred embodiment of the invention, the synthetic fibrous material used in the invention has a specific surface area of at least 0.7 m /g.

Preferably, the synthetic fibrous material contains at least 50% by weight alpha-olefin unit therein. The synthetic fibrous material may preferably be used in the support sheet in such an amount that the amount of alpha-olefin unit of said synthetic fibrous material is at least 4% by weight with respect to the total amount of the fibrous material for forming the support sheet. Typically, the synthetic fibrous material may be made of a member selected from the group consisting of polyalpha-olefin comprising at least one alpha-olefin monomer, a copolymer comprising at least one alpha-olefin monomer and at least one other copolymerizable monomer, and a mixture of a alpha-olefin polymer or copolymer with another blendable polymer and mixtures of the foregoing.

The synthetic fibrous material may be obtained by spinning a blended composition comprising at least one of alpha-olefin polymer or copolymer and at least one hydrophilic polymer. The hydrophilic polymer may be either a water soluble polymer or a copolymer of a vinyl monomer including a hydrophilic group. Alternatively, a hydrolized product of a copolymer of vinyl monomer which can take a hydrophilic group therein by hydrolysis is also useful. Typically the hydrophilic polymer is polyvinyl alcohol and the alpha-olefin polymer may be preferably polypropylene. In one of the most preferred embodiments of the invention, the synthetic fibrous material is obtained by emulsion flush spinning of a blended composition comprising polypropylene and polyvinyl alcohol.

The synthetic fibrous material may also be obtained by spinning a composition comprising a copolymer of alpha-olefin polymer with a vinyl monomer having a hydrophilic group. A hydrolysis product of a copolymer of alpha-olefin polymer with a vinyl monomer which is capable of taking therein a hydrophilic group by hydrolysis may also be used for spinning.

In another preferred embodiment of the invention, the synthetic fibrous material is synthetic fibers having a least 60% by weight of vinyl alcohol unit. The synthetic fibrous material may preferably be used in the support sheet in such an amount that the amount of the vinyl alcohol unit is at least by weight with respect to the total amount of the fibrous material. This type of synthetic fibrous material may be obtained by spinning a hydrolized vinyl acetate polymer or a hydrolized copolymer of vinyl acetate with a monomer copolymerizable therewith.

In a further preferred embodiment of the invention a modified synthetic fibrous material is used for forming the support sheet for the pressure sensitive recording system. The modified synthetic fibrous material may be obtained by carrying out the polymerization of at least one vinyl monomer on or in natural cellulose fibers. The modified synthetic material may also be obtained by depositing a polymer or copolymer comprising at least alpha-olefin monomer on natural cellulose fibers or synthetic fibers.

DETAILED DESCRIPTION OF THE INVENTION After considerable studies and experiments, we have found that the oil penetration rate of'the support sheet is an important factor in the so-called smudge and if the oil penetration rate of the support sheet material can be reduced, the pressure sensitive recording sheet can be prevented from the smudge due to the penetration of oil containing a color former. We proposed to use as an index of the oil penetration degree the coefficient of oil penetration rate which is represented by K in the following formula:

it is the length by cm of oil penetration in a test paper strip,

t is time by minutes and K is the coefficient of oil penetration rate by cm/min The above defined coefficient of oil penetration rate may be measured at a temperature of 25C, at a humidity of RH and under the atmospheric pressure of 760mmHg.

' At a matter of practice, the above defined coefficient of oil penetration rate may be measured by the following steps:

1. Preparing a test paper strip having a zero line mark;

2. Holding the test paper strip vertically;

3. Contacting the lower end of the test paper strip with tetralin (1, 2, 3, 4-tetra-hydronaphthalene);

and

4. Measuring at regular time intervals the heights or distances of the tetralin development in the test paper strip from the zero line.

It has been found that the coefficient of oil penetration rate of commercially available natural fiber paper can be reduced by a beating treatment and the heavier the beating treatment, the smaller K value the beated paper takes. However, since the beating treatment involves to remarkably reduce both the brightness and the opacity, especially, in case of natural fiber paper having such a light weight as within the range of about 30 to 5Og/m the problems mentioned before can not be resolved by applying a beating treatment to the natural fiber paper.

After a further study, it has been found that the coefficient of oil penetration rate as defined in the above can be reduced by utilizing certain synthetic fibers as a fibrous material for the support sheet. In order to attain the objects of the invention, the coefficient of tetralin penetration rate of the support sheet must be recuced to 600 X 10- cmlrnin or less. Preferably, the support sheet for the pressure sensitive recording sheet according to the invention is made of a fibrous material comprising a mixture of natural cellulose fibers with synthetic fibers, although the whole support sheet may be made of synthetic fibers alone. Preferably, the synthetic fibers used according to the invention have a specific surface area of at least 0.7 m /g.

The pressure sensitive recording paper utilizing a synthetic fiber support sheet according to the invention is superior in the effect of preventing the smudge to the known pressure sensitive recording paper utilizing a natural fiber support sheet. In addition the pressure sensitive recording paper has various improved proportions, especially, in brightness, opacity and dimensional stability against humidity such as expansion or contraction resistivity and curl resistivity. Further, according to the invention, it is possible to reduce the weight of the pressure sensitive recording paper beyond the limit which could ever be reached with the conventional pressure sensitive recording paper utilizing a natural fiber support sheet. I

It may be considered that the above mentioned improved effects and advantages according to the invention are owing to construction, affinity to oil, property of swelling by oil and other various chemical properties of synthetic fibers, independently and synergetically to each other. In some or many cases, other appropriate treatments such as addition of fillers, sizing and calendering would be effective to enhance the above mentioned effects. At any events, it should be noted that the coefficient of tatralin penetration rate of the support sheet should not be larger than 600 X l" crn/min The criticality of the coefficient of oil penetration rate will become apparent from the examples embodying the invention which will be discussed in detail hereinafter.

Useful synthetic fibers for the present invention can be selected from wide and various groups of polymers.

In a preferred embodiment of the invention, polyolefinic synthetic fibers including 50% by weight of alphaolefin unit are used for forming the support sheet. Among the polymers for polyolefinic fibers there may be included homo polymers such as polyethylen, polypropylene, poly-l-butene and poly-4-methyl-l-pentene, binary or ternary copolymers from alpha-olefin such as poly-(ethylene-propylene), binary or ternary copolymers comprising alpha-olefin and at least one other monomer copolymerizable with alpha-olefin, and graft copolymers or cross-linked products of the foregoing polymers. These synthetic resin materials may be spun by any of flush spinning, uniaxial stretching and splitting, solution shearing, emulsion flush spinning and centrifugal spinning to produce fibrous materials. Mixtures of the above mentioned polymers with each other and mixtures of those polymers with other polymers may also be used for spinning to obtain fibrous materials.

More preferably, synthetic fibers of poly-alphaolefin having a hydrophilic component are used. The spinning material for those synthetic fibers consists essentially of alpha-olefin homopolymers such as polypropylene, polyethylene, and poly-4-methylpentene-l or a copolymer produced from a mixture including at least one alpha-olefin, and of hydrophilic or water-soluble polymer component which is incorporated to the spinning material by polymer blend and/or graft-copolymerization. Among the hydrophilic or water-soluble polymer comporient to be incorporated there may be included water-soluble polymers such as polyvinyl alcohol, polyacrylamide, polyethylene oxide, polyethylene glycol and carboximethyl cellulose, random, graft or block copolymers having vinyl monomer unit having a hydrophilic radical in themselves or vinyl monomer units to which hydrophilic radical can be introduced by aftertreatment such as hydrolysis. The said hydrophilic polymer includes as well copolymers of alpha-olefin with a vinyl monomer having a hydrophylic radical in itself or a vinyl monomer to which a hydrohilic radical can be introduced by proper after-treatment. Among the vinyl monomers which have a hydrophilic group or which can take a hydrophilic group therein by a proper treatment, there may be included vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, methylmethacrylate, acrylamide, allyl alcohol and butene-tri-carboxylic acid.

Among the monomers to be introduced to polyalpha-olefin by graft polymerization, there are includee vinyl monomers having a hydroxyl group and/or a carboxyl group and vinyl monomers which can have a hydroxyl group or a carboxyl group by such a treatment as hydrolysis. For example, there may be mentioned vinyl acetate, acrylic acid, methacrylic acid, methylacrylate, methylmethacrylate, allyl alcohol and butenetricarboxylic acid. The graft polymerization product may also include any other monomer which is capable of graft copolymerization with the above mentioned vinyl monomers. For example, such monomers as acrylonitrile, vinylchloride, methylmethacrylate, acrylamide may be used in an amount less than that of the above mentioned vinyl monomer to produce a copolymerization product.

The above mentioned polymers may be spun by vari ous spinning techniques to produce fibrous material. For example, a material compound obtained by incorporating a hydrophilic component to the above mentioned alpha-olefin polymer or copolymer by blend and/or graft polymerization is dissolved in a proper solvent such as hydrocarbons or chlorinated hydrocarbons. The solution thus obtained is then added to a non-solvent with a surface active agent to produce an emulsion. The fibrous material is obtained from the emulsion thus prepared by the emulsion flush spinning technique. The fibrous material obtained by the emulsion flush spinning may be subjected to beating and/or refining, if required. The fibrous material thus obtained is easy to be fibrillated, has a relatively high specific surface area, is good in oil absorption and dispersive to water. Among the poly-alpha-olefin fibers having a hydrophilic component, there may be included, as one of the most practically useful materials, the synthetic fibrous material which is obtained by spinning through the utilization of the emulsion flush spinning technique the mixture of to 99% by weight of poly-alpha-olefin polymer or copolymer with 50 to 1% by weight of polyvinyl alcohol. The fibrous material thus obtained may be subjected to a beating treatment, if required.

The whole support sheet for the pressure sensitive recording system can be formed of the synthetic fibers essentially comprising poly-alpha-olefin without any other fibrous material. It is however also possible to form the sheet of a mixture of the above mentioned synthetic fibers with wood pulp. Any conventional paper manufacturing machine may be used. In addition to the fibrous materials inorganic fillers, sizing agents, defoaming agents, dyes and adhesives may also be used as various additives. It is desirable that the amount of alpha-olefin unit is at least 4% by weight with respect to the total amount of the fibrous material for forming the support sheet.

In another preferred embodiment of invention, the fibrous material which is used for forming the support sheet including by weight of vinyl alcohol unit. The polyvinyl alcohol resin as the spinning material may be obtained by hydrolizing a homo polymer of vinyl acetate or copolymer of a vinyl acetate monomer with a copolymerizable monomer such as vinyl chloride, acrylic ester or methacrylic ester. The spinning material comprising polyvinyl alcohol which may contain other water-soluble polymeric material such as starch, casein, cellulose derivatives, polyacrylic acid and etc. may be transformed by any conventional spinning technique to produce fibrous material. The fibrous material may be subjected to a beating treatment for fibrillation. Preferably, the support sheet manufactured utilizing this fibrous material includes 15% by weight of vinyl alcohol unit.

As a further preferred embodiment of the invention there may be modified synthetic fibrous materials. The modified fibrous material according to the invention, may be manufactured by carrying out on or in natural cellulose fibers the polymarization of at least one vinyl monomer selected from the group consisting of vinyl acetate, acrylic acid,- acrylic ester, acryl amide, methacrylic acid, methacrylic ester and methacrylamide. Alternatively, the modified fibrous material may be obtained by depositing on natural or synthetic fibers a polymer comprising at least one alpha-olefin, its copolymer or a mixture thereof.

In case of the modified fibrous material, the amount of the polymer component in the fibrous material may preferably be at least 3% by weight with respect to the total amount of the fibrous material.

The modified fibrous material may be fibrillated by a beating treatment, if required. The polymerization for producing the modified fibrous material is preferably be carried out by the solution polymerization technique, though any other polymerization techniques such as emulsion polymerization and suspension polymerization may also be utilized. The latter cases are disadvantageous in the fact that monomers are easily separated from the natural cellulose fibers. v

The most preferred one among the above mentioned three embodiments is the first one. Especially, polyalpha-olefin fibers obtained by the emulsion flush spin ning technique would be the best.

As discussed in detail in the above, the support sheet having a coefficient of oil penetration rate below the upper limit is formed of various synthetic fibers alone or of a mixture of synthetic fibers with other fibrous materials including natural cellulose fibers. The formation of the sheet may be carried out either wet or dry sheet forming technique. In the formation of the sheet, any conventional additives such as inorganic fillers, sizing agents, defoaming agents, adhesive may be used. In addition, the support sheet may be subjected to surface sizing treatment, calendering treatment and any other treatments. Among the fibrous materials which may be used together with synthetic fibers, there are included natural cellulose fibers such as wood pulp, bamboo pulp, straw pulp and linen fibers and etc. Preferably, bleached wood pulp is most economically used.

As already discussed before and will be described in detail in the following examples, it is desirable that the synthetic fibers used for forming the support sheet for the pressure sensitive record system according to the invention have a specific surface area of at least 0.7m /g. This is important to obtain a support sheet having an improved brightness and a sufficient opacity.

The definition of the specific surface area described is, per se, known and is given by the following formula:

S,,, is the specific surface area (cm /g), f is a space rate ofa sample filling layer (a fiber pad),

r is the specific gravity (g/cm) of the fibrous material,

Y is the coefficient of viscosity of air (g/cm sec),

L is the thickness of the fiber pad (cm),

Q is the volume (cm of air passing through the fiber Agis the pressure drop (g /cm between the opposite ends of the fiber pad,

A, is a cross sectional area (cm through which air passes,

t is the time (sec) required for the passing of air of Q cm through the sample layer,

W is the weight (g) of the fiber pad and A is a cross sectional area (cm of the fiber pad. In the following examples, the specific surface area of each of various samples has been calculated from the above formula after measuring the airpremeability of each of the samples at 20C and at RH. The samples have been shaped in the form of pads, made of various fibrous materials.

PREFERRED EMBODIMENTS OF THE INVENTION The following examples are given in order to illustrate the invention without limiting the same. Unless otherwise indicated, the part is shown by weight.

EXAMPLE 1 parts of LBKP (bleached hard wood kraft pulp, CSF 420 cc) and 20 parts of NBKP (bleached soft wood kraft pulp, CSF 400 cc) were mixed together to obtain a wood pulp suspension (A). On the other hand, 150 parts of powdered polypropylene was dissolved in 1000 parts of methylene dichloride in an autoclave. To the obtained solution, I900 parts of aqueous solution containing 10 parts of polyvinyl alcohol was added with 5 parts of sodium dodecylbenzenesulfonate. The said mixture solution was stirred to obtain the heated emulsion. When the temperature of the said emulsion rised up to 140C, it was flushed out from the nozzle at the bottom of autoclave. The product obtained has an appearance like a marshmallow. After stirring the obtained marshmallow-like product in a mixer for 20 minutes, a pulp suspension (B) wherein the finely fibrillated fibrous materials are homogeneously dispersed was obtained. The specific surfacd area of the said fidimensional stability to the moisture (curling, expansion and contraction) of each sample sheet were measured and the result is shown in the attached table.

The one surface of each paper sheet was coated with the capsular suspension by 5 g/m on dry basis. The preparation of the capsular suspension is as follows.

30g of.acid-treated gelatin was added to 460 g of water. The obtained mixture as heatedup to 60C to produce a solution. On the other hand, 2g of crystal violet lactone and lg of benzoylleucomethylene blue are dissolved in g of isopropyl naphthalene to produce a solution. After heated to 60C, the dye-oil solution was 9 added to the gelatin solution. An emulsion wherein oil droplets have the size of 4-5p. on the average was obtained thereby. Next, 300g of aqueous solution of gum arabic was added to the said emulsion, and then 200g of water was also added. After that, acetic acid was added to the above-obtained mixture solution to adjust pH to 44.5, and allowed the coacervates to deposite around the said oil droplet. The coacervate was gelled by cooling the above suspension to 10C. After 10g of formaldehyde was added to the above, the obtained suspension was allowed to stand for 10 hours for aging. Thus the capsular suspension was produced.

The other surface of the paper sheets was respectively coated by 8g/m on dry basis with a coating color comprising 200 parts of Water, 100 parts of active clay as acceptor, and 30 parts of styrene butadiene latex(as 50% total solid).

Yellow ink was applied onto the acceptor-coated side of the pressure-sensitive recording paper obtained by letter press. After such ink was dried the said pressuresensitive recording paper were placed one after in such a way that the capsule coated side and the acceptor coated side are in contact with each other. After the obtained set of pressure-sensitive recording paper was allowed to stand under the pressure of g/cm for 10 days, the smudge on the acceptor-coated surface was examined. The result is shown in the attached table.

Testing methods used in this invention are as follows:

Specific surface area: at 20C, 60% RH, by a gas permeameter (Shimadzu Seisakusho Ltd) Brightness: According to JIS (Japan Industrial Standard) P8123 Opacity: According to JIS P8138 Moisture Expansion and Contraction:

according to TAPPI Standard T447 m-59X (Moisture Expansivity of Paper) Curl judgement: after 24 hours in the moisture-controlled air A: Not curled B: Scarcely curled C: Curled D: Remarkably curled Smudge judgement of pressuresensitive recording paper A: No smudge appeared B: Slightly appeared C: Intensively appeared The result of the examination above shows apparently that the sheet produced from synthetic fibrous material which comprises poly-olefin and were spun by emulsion flush spinning process was remarkably improved in smudge, opacity, brightness, expansion, contraction and curl at the same time.

In the following examples, the property test of support sheet and pressure-sensitive recording paper was carried out in the same manner as in Example 1, and the producing method of pressure-sensitive recording paper was also the same as that of Example 1.

EXAMPLE 2 A blended polymer composition consisting of 15% of partially saponified polyvinyl acetate and 85% isotactic polypropylene having melt flow index of 8 was extruded, and the obtained film was drawn 14 times in 10 refined in a laboratory Niagara Beater for 3 hours with 4 gram of nonionic surface active agent and 25 l of water to produce a split fiber (C) with length of 1.0 2.0 mm and width of 10 30 microns. The specific surface area of the said fiber was 0.89 m /g.

The obtained polypropylene split fiber (C) was mixed with the wood pulp suspension (A) used in Example l in the blending ratio (A)/(C) of /15, 75/25 and 65/35 on the basis of dry weight to obtain pulp suspensions. The pulp suspensions were respectively applied to TAPPI Sheet Machine to obtain support sheets (c-l, c-2, and c-3) of 4Og/m on dry basis.

On the other hand, to compare with the aboveobtained sheets, a split fiber (D) was produced from a melt of isotactic polypropylene in the same manner as above. Length, width adn specific surface area of the obtained split fiber (D) were respectively 1.0 2.5mm, l0 40 microns and 0.64 m /g. Furthermore, a melt of the above isotactic polypropylene having melt flow index of 8 was spun. After the extrusion was taken into the water for cooling, the said extrusion was drawn 10 times with three rolls in C water bath to produce a filament of 3 denier. The filament was cut into 3 mm in length. The specific surface area of the obtained fibrous material (E) was 0.35 m /g.

The obtained fibrous material (D) and (E) were respectively mixed with the wood pulp suspension (A) in the blending ratio above to obtain paper sheets (d-l, d-2, d-3; e-l, e-2, e-3). Each sheet obtained above and pressure-sensitive recording paper produced with use of the said sheet were tested and the results are shown in the attached table.

EXAMPLE 3 130 parts of powdered polyethylene and 420 parts of hexane were placed in an autoclave and were heated to 200C with stirring to produce a solution. The solution was flushed out from a nozzle under the pressure of 60 kg/cm G to produce a fibrous material which was subsequently refined to have the specific surface area of 2.0m /g.

The obtained fibrous material (F) was then mixed with the wood pulp suspension (A) used in Example 1 in the blending ratio (A)/(F) of 50/50, 20/80 and 0/100 on the basis of dry weight to obtain pulp suspensions. The obtained pulp suspensions were respectively applied to TAPPI Sheet Machine to produce paper sheets (f-l, f-2, f-3) of 40 g/m on the dry basis. Each sheet obtained above and the pressure-sensitive recording paper produced with use of the said sheet were tested and the results are shown in the attached table.

EXAMPLE 4 An emulsion consisting of the chemicals below was flushed in the same manner in Example 1.

Chlorinated polypropylene 23 parts Polypropylene parts Polyethylene 30 parts Polyvinyl alcohol 18 pans Methylene dichloride 1000 parts Water 1800 parts Sodium dodecylbenzenesulfonate 5 pans The product, appearance of which is like a marshmallow, was diluted with water into the concentration of 2% and stirred for 20 minutes in a mixer to obtain a finely fibrillated fibrous material (G), specific surface area of which was 7.1 m /g. The said fibrous material (G) and the wood pulp suspension (A) used in Example 1 were mixed together in the blending ratio (A)/(G) of 75/25, 50/50 and 25/75 to obtain pulp suspensions. Each pulp suspension was applied to TAPPI Sheet Machine to produce paper sheet (g-l, g-2, g-3) of 40 g/m on dry basis. Each sheet obtained above and pressure-sensitive recording paper produced with use of the said sheet were tested and the results are shown inthe attached table.

EXAMPLE 5 An aqueous solution containing 14% polyvinyl alcohol (PVA) having average polymerization degree of 1500 and 30% starch on PVA was spun and drawn by 250% with roller in an aqueous solution (50C) saturated with sodium sulfate. Consequently the second drawing by 60% was carried out in a solution (80C) saturated with sodium sulfate. After drying the drawn fiber, the third drawing by 60% was carried out in the air of 225C and the heat-setting was carried out without any draft.

The above-obtained fiber of 1 denier was cut into 3 mm in length and refined by PFl mill to obtain fibrous material (H) having the specific surface area of 2.1 m /g.

Thus obtained fibrous material (H) was mixed with the wood pulp suspension (A) used in Example 1 in the blending ratio (A)/(1-1) of 80/20 and 65/35. The obtained pulp suspensions were respectively applied to TAPPl Sheet Machine to produce paper sheet (h-l,

12 h-2) of g/m on dry basis. Each sheet thus obtained and the pressure-sensitive recording paper produced with use of the said sheet were tested and the results are shown in the attached table.

EXAMPLE 6 Polyethylene emulsion was added to the aqueous suspension of LBKP (CSF 465 cc) with a proper amount of aluminum sulfate to deposit on the surface of LBKP. The amount of deposited polyethylene was nearly equivalent on dry basis to that of the pulp suspension. The specific surface area of the obtained modified fibrous materials (1) was l.6m /g. Paper sheets (i) of 40 g/m on dry basis were produced form the modified fibrous material above in the same manner as in Example 1. The sheet thus obtained and the pressure-sensitive recording paper produced with use of the said sheet were tested and the results are shown in the attached table.

EXAMPLE 7 Modified fibrous material (J) was produced in the same manner as in Example 6 except that acryl fibers (CSF 300 cc) was used instead of LBKP. The specific surface area of the said fibrous material was 2.0 mlg. Paper sheets of 40 g/m on dry basis were produced from the above-obtained fibrous material in the same manner as in Example 1. Sheet thus obtained and the pressure-sensitive recording paper produced with use of the said sheet are tested and the results are shown in the attached table.

TABLE Sample Blending Rate Bright- Opacity Dimensional stability to the moisture Smudge of sheet ratio (parts of oil ness pressureby weight) penet- 65%RH 95%RH 65%RH 10%RH sensitive ration recording K(cm/min) Expansion(%) Curl Contract Curl paper Control a A/B X10 example 100/0 740 78.8 67.9 0.65 0 0.56 D C b-l 93/7 410 81.8 72.5 0.45 B 0.41 B B b-2 85/15 128 83.0 75.3 0.35 B 0.32 B A Example 1 b-3 75/25 84.3 80.4 0.29 B 0.25 B A b-4 /35 35 85.0 84.1 0.25 B 0.18 B A b-5 0/100 0 89.5 90.3 0.01 A 0.01 A A A/C Example 2 c-l 85/15 416 82.0 71.4 0.44 B 0.40 B B c-2 /25 250 82.7 71.3 0.40 B 0.35 B B c-3 65/35 226 83.5 73.7 0.30 A 0.28 B A A/D Control d-l 85/15 765 77.5 67.5 0.54 C 0.50 C C example d-2 75/25 710 80.3 67.8 0.52 B 0.49 B C d-3 65/35 660 81.5 68.6 0.45 B 0.42 B C /E e-l 85/15 830 80.0 65.3 0.44 C 0.41 C C e- 75/25 720 80.3 66.0 0.33 B 0.30 B C e- 65/35 700 79.3 66.3 0.32 B 0.29 B C A/F Example 3 f-l 50/50 570 86.2 78.2 0.40 B 0.37 B B f-2 20/80 405 88.7 81.8 0.25 A 0.21 A B f-3 0/100 210 90.0 81.3 0.13 A 0.11 A A A/G Example 4 g-l 75/25 350 79.0 75.5 0.27 B 0.20 A A g-2 50/50 154 81.5 79.0 0.23 A 0.19 A A g-3 25/75 48 86.0 85.3 0.10 A 0.09 A A /H Example 5 h-l /20 540 79.0 69.3 0.48 B 0.43 B B h-2 65/35 280 80.3 71.5 0.35 B 0.32 B A All Example 6 i 0/100 455 79.3 68.1 0.35 B 0.31 B B All Example 7 0/100 590 79.0 68.1 0.42 B 0.39 B B What we claim is:

1. A pressure sensitive recording paper comprising a support sheet having, disposed on at least one of the surfaces thereof, at least one color producing reactant selected from the group consisting of a colorless dye material which is dissolved in an oil and contained in microcapsules and a color acceptor reactive with said colorless dye material to produce a color image, said support sheet comprising fibrous material, at least a part of which is synthetic fibrous material, said synthetic fibrous material being selected from the group consisting of (l synthetic fibers made of an alpha-olefin polymer or copolymer; (2) synthetic fibers made of a mixture of an alpha-olefin polymer or copolymer with another blendable polymer; (3) synthetic fibers having at least 60% by weight of vinyl alcohol unit; (4) modified synthetic fibers obtained bycarrying out polymerization of at least vinyl monomer on or in natural cellulose fibers; and (5) modified synthetic fibers obtained by depositing an alpha-olefin polymer or copolymer on natural or synthetic fibers, and said support sheet having a coefficient of tetralin penetration rate of 600 X cm/min or less, said coefficient of tetralin penetration rate being represented by K in the following formula:

h(cm) K VT) wherein h is a length by cm of tetralin penetration and z is time by minute.

2. A'pressure sensitive recording paper as defined in claim 1, in which said fibrous material consists ofa synthetic fibrous material.

3. A pressure sensitive recording paper as defined in claim 1, in which said fibrous material comprises a mixture of a synthetic fibrous material with a natural cellulose fibrous material.

4. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material has a specific surface area of at least 0.7m /g.

5. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material contains at least 50% by weight of alpha-olefin unit therein.

6. A pressure sensitive recording paper as defined in claim 5 in which the synthetic fibrous material is used in said support sheet in such an amount that the amount of said alpha-olefin unit of said synthetic fibrous material is at least 4% by weight with respect to the total amount of the fibrous material forming said support sheet.

7. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material is obtained by spinning a blended composition comprising at least one alpha-olefin polymer or copolymer and at least one hydrophilic polymer.

8. A pressure sensitive recording paper as defined in claim 7, in which said hydrophilic polymer is a member selected from the group consisting of a water soluble polymer, a copolymer of vinyl monomer including a hydrophilic group and a hydrolized copolymer of vinyl monomer which can take a hydrophilic group therein by hydrolysis.

9. A pressure sensitive recording paper as defined in claim 8, in which said hydrophilic polymer is poly-vinyl alcohol.

10. A pressure sensitive recording paper as defined in claim 7, in which said alpha-olefin polymer is polypropylene.

11. A pressure sensitive recording paper as defined in claim 7, in which said synthetic fibrous material is obtained by the emulsion flush spinning ofa blended composition comprising polypropylene and polyvinyl alcohol.

12. A pressure-sensitive recording paper as defined in claim 1, in which said synthetic fibrous material is obtained by spinning a composition comprising a copolymer of alpha-olefin with a vinyl monomer having a hydrophilic group or a hydrolysis product of a copolymer of alpha-olefin with a vinyl monomer which is capable of taking therein a hydrophilic group by hydrolysis.

13. A pressure sensitive recording paper as defined in claim 1, in which the syntheticfibrous material is used in said support sheet in such an amount that the amount of said vinyl alcohol unit of said synthetic fibrous material is at least 15% by weight with respect to the total amount of the fibrous material forming said support sheet.

14. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material is obtained by spinning a composition comprising a member selected from the group consisting of a hydrolized vinyl acetate polymer and a hydrolized copolymer of vinyl acetate with a monomer copolymerizable therewith.

15. A pressure sensitive recording paper as defined in claim 14, in which said monomer copolymerizable with vinyl acetate is selected from the group consisting of vinyl chloride, acrylic ester and methacrylic ester.

16. A pressure sensitive recording paper as defined in claim 1, in which the said amount of the polymer component in said modified fibrous material is at least 3% by weight with respect to the total amount of said fibrous material. 

1. A PRESSURE SENSITIVE RECORDING PAPER COMPRISING A SUPPORT SHEET HAVING, DISPOSED ON AT LEAST ONE OF THE SURFACES THEREOF, AT LAST ONE COLOR PRODUCING REACTANT SELECTED FROM THE GROUP CONSISTING OF A COLORLESS DYE MATERIAL WHICH IS DISSOLVED IN AN OIL AND CONTAINED IN MICROCAPSULES AND A COLOR ACCEPTOR REACTIVE WITH SAID COLORLESS DYE MATERIAL TO PRODUCE A COLOR IMAGE, SAID SUPPORT SHEET COMPRISING FIBROUS MATERIAL, AT LEAST A PART OF WHICH IS SYNTHETIC FIBROUS MATERIAL, SAID SYNTHETIC FIBROUS MATERIAL BEING SELECTED FROM THE GROP CONSISTING OF (1) SYNTHETIC FIBERS MADE OF AN ALPHA-OLEFIN POLYMER OR COPOLYMER; (2) SYNTHETIC FIBERS MADE OF A MIXTURE OF AN ALPHA-OLEFIN POLYMER OR COPOLYMER WITH ANOTHER BLENDABLE POLYMER, (3) SYNTHETIC FIBERS HAVING AT LEAST 60% BY WEIGHT OF VINYL ALCOHOL UNIT; (4) MODIFIED SYNTHETIC FIBERS OBTAINED BY CARRYING OUT POLYMERIZATION OF AT LEAST VINYL MONOMER ON A IN NATURAL CELLULOSE FIBERS; AND (5) MODIFIED SYNTHETIC FIBERS OBTAINED BY DEPOSITING AN ALPHA-OLEFIN POLYMER OR COPOLYMER ON NATURAL OR SYNTHETIC FIBERS, AND SAID SUPPORT SHEET HAVING A COEFFICIENT OF TETRALIN PENETRATION RATE OF 600 X 10**-3 CM/MIN 1/2 OR LESS, SAID COEFFICIENT OF TETRALIN PENETRATION RATE BEING REPRESENTED BY K IN THE FOLLOWING FORMULA: H(CM) = K((T(MIN)**1/2) WHEREIN H IS A LENGTH BY CM OF TETRALIN PENETRATION AND T IS TIME BY MINUTE.
 2. A pressure sensitive recording paper as defined in claim 1, in which said fibrous material consists of a synthetic fibrous material.
 3. A pressure sensitive recording paper as defined in claim 1, in which said fibrous material comprises a mixture of a synthetic fibrous material with a natural cellulose fibrous material.
 4. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material has a specific surface area of at least 0.7m2/g.
 5. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material contains at least 50% by weight of alpha-olefin unit therein.
 6. A pressure sensitive recording paper as defined in claim 5, in which the synthetic fibrous material is used in said support sheet in such an amount that the amount of said alpha-olefin unit of said synthetic fibrous material is at least 4% by weight with respect to the total amount of the fibrous material forming said support sheet.
 7. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material is obtained by spinning a blended composition comPrising at least one alpha-olefin polymer or copolymer and at least one hydrophilic polymer.
 8. A pressure sensitive recording paper as defined in claim 7, in which said hydrophilic polymer is a member selected from the group consisting of a water soluble polymer, a copolymer of vinyl monomer including a hydrophilic group and a hydrolized copolymer of vinyl monomer which can take a hydrophilic group therein by hydrolysis.
 9. A pressure sensitive recording paper as defined in claim 8, in which said hydrophilic polymer is poly-vinyl alcohol.
 10. A pressure sensitive recording paper as defined in claim 7, in which said alpha-olefin polymer is polypropylene.
 11. A pressure sensitive recording paper as defined in claim 7, in which said synthetic fibrous material is obtained by the emulsion flush spinning of a blended composition comprising polypropylene and polyvinyl alcohol.
 12. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material is obtained by spinning a composition comprising a copolymer of alpha-olefin with a vinyl monomer having a hydrophilic group or a hydrolysis product of a copolymer of alpha-olefin with a vinyl monomer which is capable of taking therein a hydrophilic group by hydrolysis.
 13. A pressure sensitive recording paper as defined in claim 1, in which the synthetic fibrous material is used in said support sheet in such an amount that the amount of said vinyl alcohol unit of said synthetic fibrous material is at least 15% by weight with respect to the total amount of the fibrous material forming said support sheet.
 14. A pressure sensitive recording paper as defined in claim 1, in which said synthetic fibrous material is obtained by spinning a composition comprising a member selected from the group consisting of a hydrolized vinyl acetate polymer and a hydrolized copolymer of vinyl acetate with a monomer copolymerizable therewith.
 15. A pressure sensitive recording paper as defined in claim 14, in which said monomer copolymerizable with vinyl acetate is selected from the group consisting of vinyl chloride, acrylic ester and methacrylic ester.
 16. A pressure sensitive recording paper as defined in claim 1, in which the said amount of the polymer component in said modified fibrous material is at least 3% by weight with respect to the total amount of said fibrous material. 